Novel tetrafluoroethylene resins and their preparation



United States Patent 3,142,665 NOVEL TETRAFLUOROETHYLENE RESINS ANDTHEIR PREPARATION Anthony John Cardinal, Parkersburg, and William LeeEdens, Vienna, W. Va, and .lohn Wiiiiam van Dylr, Wilmington, Del.,assignors to E. I. du Pont de Nemours and Company, Wilmington, DeL, acorporation of Delaware N0 Drawing. Filed July 26, 1960, Ser. No. 41,711

11 Claims. (Cl. 260-92.1)

This invention relates to a class of particulate tetrafiuoroethyleneresins, comprising at least 98 weight percent combinedtetrafluoroethylene, predominantly comprising spheroidal particles 0.05to 0.5 micron in diameter, having an average particle diameter in therange of 0.12 to 0.35 micron, a standard specific gravity of less than2.235 and a specific melt viscosity of greater than 1 l0 poises at 380C., hereinafter referred to as high molecular weight dispersion resins.

Resins having the aforesaid characteristics are commercially availableas aqueous colloidal dispersions, obtained by polymerizingtetrafiuoroethylene in media consisting essentially of water, initiatorand dispersing agent, and as fine powders, obtained by coagulating suchdispersions under low shear stress conditions. The resins are useful inthe manufacture of thin-walled articles. Thus the dispersions as suchare used for impregnating, casting and coating, usually followed bysintering to coalesce the resin particles. The fine powders are used inthe fabrication by paste extrusion techniques of continuous thin-walledarticles such as wire coatings, tapes, films, tubes, pipes and the like.The articles are valuable by reason of their outstanding resistance toweather, heat, friction, electricity, chemicals and mechanical stress.

In paste extrusion, fine powder is blended with lubricant to form apasty mass which is charged to an extruder barrel and extruded through adie of reduced cross-sectional diameter. The resulting extrudate is thenusually heated and sintered to remove lubricant and coalesce theresidual resin into an integral mass. High molecular Weight dispersionresins have hitherto been unsatisfactory in a number of paste extrusionapplications, owing to their tendency to develop shear faults whenextruded at high reduction ratios, i.e., under conditions where thecross-sectional area of the extruder barrel is relatively large incomparison to the cross-sectional area of the extruded article. For thisreason, such resins have not hitherto been suitable for standardizedpaste extrusion at reduction ratios of 1600 to 1 or more, and moreover,have tended to develop an undesirable number of flaws, even at lowerreduction ratios, when extruded into articles of considerable length.

According to the present invention, there are provided new highmolecular weight dispersion resins obtained by polymerizingtetrafiuoroethylene in an aqueous medium consisting essentially ofwater, initiator, and dispersing agent, distinguished in that the mediumalso contains, at least during the polymerization of the final 30% ofthe etrafluoroethylene polymerized, a modifier effective to maintain theoverall rate of polymerization at least percent below that obtaining forthe polymerization of an equal quantity of tetrafiuoroethylene in anidentical reaction medium continuously saturated withtetrafiuoroethylene at the same temperature and pressure in the absenceof said modifier, said modifier consisting of one or more members of thegroup consisting of water-soluble non-polymerizable chain transferagents containing at least one covalently-bound non-metallic monovalentatom other than fluorine, perfluoroalkyl-trifluoroethylenes of 3 to 10carbon atoms, and oxyperfluoroalkyl-trifiuoroethylenes of 3 to 10 carbonatoms.

3,142,655 Patented July 28, 1964 The new resins have not only theadvantageous characteristics of earlier high molecular Weight dispersionresins, but also improved paste extrudability. In specific aspects theyare further characterized by a narrow particle size distribution suchthat Ad /2 /d the ratio, to average particle diameter, of the spread inparticle diameters at the half-peak concentrations of particle sizes byweight, is less than 0.40; by a distribution of molecular weight alongthe particle radii such that the ratio of molecular weight of the shellhalf to the molecular Weight of the core half of the particles is lessthan 3.5; or by the presence of very small amounts, in the range of 0.01to- 0.3 weight percent, of combined perfluoroalkyloroxyperfiuoroalkyl-trifiuoroethylene in at least the outer 30 weightpercent of the resin particles as determined by infrared measurement; orby a combination of two or more such features. In preferred aspects theyare capable of being paste extruded at reduction ratios of at least 1600to 1.

In the preparation of the new resins the procedures used are basicallythose hitherto known to produce high molecular weight dispersion resins.The aqueous medium containing initiator and dispersing agent is chargedto an evacuated stirred reactor and continuously pressured withtetrafiuoroethylene until the desired quantity of dispersion resin isobtained. The same ranges of temperature, pressure, choice of initiatorand dispersing agent, type of reactor and proportions of ingredients:are employed. The use of a modifier in accordance with the presentinvention is effective in aqueous media continuously saturated withtetrafiuoroethylene to reduce the overall reaction rate by at least 5percent and preferably not more than 50 percent without concomitantlycausing a change in the fundamental classification of the resinproduced. The relative rates in the presence and absence of modifierreferred to are the average rates obtained in polymerizing equalquantities of tetrafiuoroethylene in identically constituted aqueousmedia at the same temperature and pressure. Comparisons made in this wayprovide a measure of the inhibiting effect of the modifier. in theactual practice of the present invention, however, the stirring providedmay be insufiicient to maintain the reaction medium continuouslysaturated with respect to monomer, and the overall reaction rate will becorrespondingly limited. Under such conditions, the presence of themodifier in accordance with the invention may occasion little or nochange in the observed overall reaction rate, but is neverthelessessential and operable to produce the desired new resins.

Advantageously, when operating under conditions such that the presenceof modifier does produce an observable decrease in reaction rate, highlyactive initiators are used at relatively low temperatures in order toobtain maximum reaction rates consistent with the retention of a highlevel of molecular weight. Thus, in the systems under consideration,active initiators such as ammonium or potassium persulfate at lowtemperature appear to provide equally good chain initiating and chainpropagating activity, but concomitantly less chain terminating activity,as compared with less active initiators such as disuccinic acid peroxideat higher temperature, with the net effect that higher overallpolymerization rates are achieved. The retardation of rate which may beoccasioned by the use of modifiers in accordance with the presentinvention can thus be counterbalanced by the use of active initiators atlow temperature, so that economical overall rates are obtained.

The chain transfer agents which may be used as modifiers in accordancewith the present invention contain covalently-bound hydrogen or halogenother than fiuo- 3 To facilitate their use in proper amounts, they arepreferably liquids of moderate chain transfer activity, soluble in thereaction medium over a broad range of temperatures and pressures.Methanol is especially preferred. Examples of other effective chaintransfer agents include hydrogen, methane, ethane, propane, propylene,carbon tetrachloride, dichlorotetrafluoroethane, bromoform, acetone andpropionic acid. The use of chain transfer agents as sole modifiers inaccordance with the present invention provides resins of exceptionallygood thermal stability.

Perfiuoroalkyland oxyperfiuoroalkyl-trifiuoroethylcues of 3 to carbonatoms may be used as modifiers in accordance with the present inventioneither alone to provide resins having outstanding fiexural properties,or together with a chain transfer agent to provide resins which arepaste extrudable at very high reduction ratios, on the order of 10,000/1or more. The lower-carbon trifluoroethylenes are preferred for optimumheat aging and paste extmdability properties; hexafluoropropylene isespecially preferred for optimum sintering characteristics.

The proportions or modifier employed will vary widely in accordance withthe activity of the particular modifier chosen, and also with thetemperature and pressure. With normally gaseous modifiers the minimumamounts required to obtain effective rate limiting capacity ordinarilyrange from about 0.1 part per million with a highly active modifier suchas propane to 10,000 parts per million for a very mildly active modifiersuch as pentafiuoroethane, based on the weight of monomer charged.Correspondingly, with normally liquid modifiers, these amountsordinarily are in the range of 10 to 5000 parts per million, based onthe weight of the aqueous medium. However, amounts larger than theseminima, in instances up to 30,000 parts per million or more based onmonomer, may also be employed.

The modifiers may effectively be incorporated into the reaction mixturewhen about 70 percent of the total quantity of the tetrafluoroethyleneto be polymerized has reacted, or at any earlier stage of the reaction.Presence of modifiers throughout the polymerization reaction favors anarrow particle size distribution, and therefore somewhat better pasteextrudability. Presence of modifier only during polymerization of thefinal 30 percent of tetrafiuoroethylene on the other hand favors ahigher overall reaction rate. Except as effective modifier is presentduring this final stage of the reaction, however, the benefits of thepresent invention are not obtained. It is believed that the presence ofthe modifier during this stage counterbalances the tendency for thegrowing particles to develop very long-chain, highly crystalline shells.

While the reaction medium of the present invention consists essentiallyof water, initiator, dispersing agent and modifier, various otheringredients may also be present without deleterious results as hithertoknown in the art. The charge thus preferably includes a saturatedhydrocarbon wax, which is not active as a chain transfer agent, tofacilitate the preparation of non-agglomerated dispersions of highsolids content. Similarly, when it is desired to prepare resins whichmanifest a lower paste extrusion pressure, the reaction medium may beseeded with pre-made colloidal particles of polytetrafiuoroethylene,which favors the production of large particles, at some expense in theuniformity of particles size distribution.

The proportion of spheroidal particles, the average particle diameters,and the distribution of particle sizes by weight as referred to hereinmay be determined directly by examination of photographs of samplesunder the electron microscope at 20,000 diameters magnification. Theaverage particle diameter (d may also be determined indirectly by arelationship based on light-scattering theory, from the percentage ofincident light transmitted at 546 millimicron wave length through a unitmeasure of a dilute dispersion (ca. 0.02 weight percent solids),corrected to accord with the values obtained via the electronmicroscope. The distribution of particle sizes by weight may also bedetermined indirectly by an ultra-centrifuge analysis of dispersion inwhich a photograph representing the changes of refractive index (RI)across the boundary region between the aqueous medium and the bulk ofcolloidal dispersion particles of polytetrafiuoroethylene sedimentingunder the influence of centrifugal force is analyzed using a travellingmicroscope. These changes in R1 are converted to changes in weightconcentration across the boundary on the assumption that the specificrefractive index increment for the dispersion particles relative to theaqueous medium is independent of particle size. By applying Stokesrelationship and assuming that all particles are spherical and ofdensity 2.295 g./cc., difierential distribution as a function ofparticle size is obtained, and corrected if necessary to accord with theweight distribution curve derived from an analysis of photographs takenwith the electron icrcscope. A horizontal line is drawn which bisectsthe maximum ordinate of the distribution curve so obtained. Thedifference, Ad /Z, between the abscissa values, in microns, of the twointersections of this line with the curve, divided by the weight-averageparticle size, d also in microns, is a convenient measure of therelative width of the particle size distribution. Resins having a ratio,AdVz/d of less than 0.40 are preferred.

The standard specific gravity (SSG) of the resins discussed herein isdetermined by the ratio of weight in air to weight of an equal volume ofwater, at 23 C. of a specimen prepared in a standard manner. In thestandard specimen preparation, a 3.5 gram sample of dry resin powder isleveled between aluminum foils, in a cylindrical mold 2.73 cm. indiameter, and pressure is gradually applied during about 30 seconds to afinal pressure of about 352 kg./cm. which is held for two minutes. Theresulting preform is baked in an air oven at 380 C. for 30 minutes,cooled to 300 C. at a rate of 1 C. per minute, removed from the oven,and then conditioned for 3 hours at 23 C. The standard specific gravityso obtained is a rough measure of average molecular weight. In the caseof tetrafiuoroethylene resins prepared in the absence of modifier or inthe'presence of chain transfer agent as the sole modifier, empiricalcorrelations from kinetic considerations indicate the relationshipSSG=2.612-0.582 log H where fi is the number average molecular weight.

The shell-to-core ratio of number-average molecular Weight as discussedherein is calculated from the M of the half Resins having a. Value OfZIn of less than 3.5 are preferred.

The specific melt viscosity at 380 C. (MV as discussed herein is a valuein poises determined from the rate at which a sample of resin extrudesunder a shear stress of 4.5 X 10 dynes/cm. by the procedure disclosed inBelgian Patent 560,454, granted September 14, 1957.

5 The combined hexafiuoropropylene content as discussed herein is aweight percent value obtained by infra-red absorbance. The value is theproduce of 0.3 and the ratio of absorbance in the infra-red, of acold-pressed sample of the resin 0.05 cm. thick, at 10.18 microns to theinfra-red absorbance of the same sample at 10.7 microns. To determinethe hexafluoropropylene content in the shell portion of the resinparticles, the hexafiuoropropylene content of the core portion isdetermined and compared with the hexafiuoropropylene content of thefinal resin, in the manner described above for determination of theshell-to-core relationship of molecular weight.

The paste extrusion performance (EP) of various resins as discussedherein is determined by a standardized procedure wherein 81 parts byweight of fine powder are admixed with 19 parts by Weight of ahydrocarbon lubricant, predominantly comprising decane and undecane, andhaving a viscosity of about 1.36 centipoises at 25 C. and a boilingrange of 175208 C. The mixture is rolled at 30 r.p.rn. for 20 minutes ina cylindrical vessel, having a water capacity of about 500 parts, toeifect blending. The blend is compacted under hand pressure into acylinder 3.16 cm. in internal diameter, and from thence extruded at 30C., and at a uniform rate of 23.5 grams per minute, through a dieconically tapering at an apex angle of 60 to a cylindrical orifice 0.08cm. in internal diameter, and 0.038 cm. in axial length. The quality ofthe extrudate is visually rated as F for discontinuous extrudate andfrom to 10 for continuous extrudate of from very poor to excellentregularity and freedom from flaws. Pressure required is also recordedand is preferably in the range of 250 to 1000 kg./sq. cm.

The invention is more particularly illustrated and explained by means ofthe following comparisons and examples, which are not intended to belimiting. In the examples and comparisons all parts and percentages areby weight except as otherwise noted. In the examples, APS is ammoniumpersulfate, KPS is potassium persulfate; DSP represents disuccinic acidperoxide,

(HOOCCH CH CO 0 used together with 2 parts per million of powdered ironExcept as otherwise specified, the values given for average dispersionparticle size are uncorrected results obtained by the aforementionedlight-transmission analysis based on an assumed value of 0.020 cc./ g.for the refractive index increment of colloidal particles ofpolytetrafluoroethylene dispersed in an aqueous medium at 25 C. Thevalues so reported differ from the average particle sizes determinedfrom electron microscope photographs or by ultra-centrifuge analysis byabout 20 to 10 +30% depending on the degree to which the actualrefractive index increment is different from 0.020 cc./g. and on thedegree of agglomeration of the colloidal particles in the dispersion.

EXAMPLES 1 TO 12 A horizontally-disposed, water-steam jacketed,cylindrical stainless steel autoclave, having a paddlewheel agitatorrunning the length of the autoclave, and having a length-to-diameterratio of about 10 to 1 and a water capacity of 3900 parts, is evacuated,charged with 1500 parts of demineralized deoxygenated water, and withdesired concentrations of dispersing agent and initiator based on theweight of the Water. The liquid modifier is charged in the indicatedconcentration in percent by weight, based on water, to the aqueous phaseand is present throughout the reaction. The charge is then pressuredwith about 2 atmospheres of tetrafluoroethylene, stirred at 125 r.p.m.to keep the aqueous phase saturated with tetrafiuoroethylene, heated todesired reaction temperature, and further pressured to 28.2 atmospheresabsolute with tetrafiuoroethylene. Stirring and temperature are thenmaintained until reaction commences, as evidenced by a drop in pressure,and then further maintained, while continuously maintaining pressure at28.2 atmosdiluted and coagulated by the procedure of I. F. Lontz U.S.Patent 2,593,583, issued April 22, 1952. Samples standard pasteextrusion performance (EP). Results are of the products are lubricatedand extruded to determine summarized in Table I.

Table I Initiator Dispersing Extrusion Reaction Agent Overall PercentPerformance Example Tem- Percent Percent Reaction Solids N0. pera- Modi-Wax Rate, in Disd.3 SSG ture, fier* g./liter/ persion Extrusion Extru-Kind Percent C. Kind Percent hour Pressure, date kg./cm. Quality 0. 048C APFCU 0. 15 0. 01 6. 3 337 35. 2 0. 161 2. 218 660 6 0. 006 C APFC 0.15 0. 01 6. 3 290 35. 0 0. 136 2. 220 670 9 0.012 60 CsAPFC 0. 15 0.016. 3 396 40. 5 0.130 2. 221 730 6 0.012 60 CsAPFC 0. 15 0.009 6. 3 48041. 2 0. 141 2. 220 625 9 0.012 60 CaAPFG 0.15 0.02 6. 3 205 36. 9 0.1452. 234 610 8 0. 024 60 CEAPFO 0. l5 0. 01 6. 3 585 34. 5 0. 157 2. 221705 7 0. 006 60 09111 0... 0. 15 0.009 6. 3 550 39. 7 0.185 2. 206 465 90. 006 60 CQAFO 0. 15 0.011 6.3 515 40. 6 0. 184 2. 220 400 9 0. 009 60C9AFC 0.15 0.010 6. 3 510 40. 3 0.179 2. 212 420 10 0. 006 70 OQAFC. 0.15 0.009 6. 3 770 40. 5 0. 230 2. 229 330 9 0. 1 85 CSAPF G. O. 214 O.045 6. 3 435 30. 8 0.156 2. 224 595 8 0.1 85 CEAPFO 0. 214 0. 09 6. 3367 30. 8 0. 152 2. 231 650 8 *Runs 1 to 10, methanol modifier.

Runs 11 and 12, propionic acid modifier.

In comparison runs under identical conditions in the absence ofmodifier, it was found that identical quantities of high molecularweight dispersion resins were obtained at rates of from 1.2 to 2 timesas great as in the examples,

but that in each instance, the resins obtained yielded only fracturedextrudates in the extrusion performance test.

EXAMPLES 13 to 23 The procedure of Examples 1 to 12 is repeated exceptthat in these cases HFP modifier was premixed with thetetrafluoroethylene to be charged, in the concentration indicated inweight percent based on tetrafluoroethylene,

and thus continuously charged to the reaction. Also, in Examples 17, 18,and 19, the concentrations of tetrafluoroethylene in the aqueous mediawere continuously maintained slightly below the saturation point. Theresults 8 EXAMPLE 25 The general procedure of Examples 13 to 23 isrepeated, but operating at less than saturated conditions, in

are summarized in Table II. 5 a different reactor of somewhat largersize, having a Table II Initiator Dispersing Extrusion Reaction AgentOverall Percent Performance Example Tem- Percent Percent Reaction SolidsN o. pera- Modi- Wax Rate, in Disd, SSG

tore, fier* ,gJliter/ persion Extrusion Extru- Kind Percent C. KindPercent hour Pressure, date kg/cmfi Quality 0.1 35 C APFC. 0.15 0.15 6.3523 35 0.170 2.205 455 s 0.1 35 GSAPFC 0.15 0.5 6.3 475 35 0.133 2. 203335 6 0.1 35 .GSAPFO 0.15 0.75 6.3 441 35 0.100 2.202 455 10 0.1 85GBAPFO 0.75 0.9 6.3 522 35 0.143 2.194 935 8 *Hexafluoropropylene(I-IFP) In comparison runs under identical conditions in the length-tYatiO 0f t0 the aqueous C a g absence of modifier, it was found thatexcept under the o upying one-half the reactor volume, and containingconditions of Examples 17, 18, and 19, identical quanti- W ig t percentDSP, 0.15 weight percent C AFC, ties of high molecular weight dispersionresins were oba P r ent of paraflin wax. The charge was prestained atrates of from 1.2 to 2 times as great as in the sured to 28.2 atmosph rs absolute with tetl'aflllomethylr examples. Under the conditions of 17,18, and 19 the 6H6 Containing 2 W g t p r ent HFP, and thereafter onlyrates were substantially unchanged in the absence ofmoditetfafium'ofithylene was g After 80 Percent Of the fiers. In allcomparison runs, the products yielded only total TetFFJ-flum@T-hY1en6was Polymefimd, pp y of tetrafractured extrudates in the extrusionperformance test. fluoroethylene was pp the Pressure w d t 16- Infurther comparison runs under the identical conditions crease to 13atmospheres absolute, and the run was then of Examples 17, 18, and 19 inwhich the aqueous charges tfil'mmaied- The fesldual gas C0ntaiI 1Bdwelght P were maintained continuously saturated with tetrafluorocent TheProduct, of 35 welght Percent Solids, ethylene, reaction rates 1.2 to1.5 times greater were obw Obtained at an Ov rall reaction rate of 490grams/ tained in the absence of modifiers, and these products also 40liter/hour, had an average P8111616 SIZE 0f micron, fractured in theextrusion performance test. Infra-red and an SSG of In the eXffllsionPerformance test, analyses of the products of the examples indicatedcomeXtYPdate 0f q y 3 8? o ta n d at kg ./cm. exbinedhexafluoropropylene contents of less than 0.2 Weight tYuSlOB pfessure-Under ldentlcal COHdlUOIlS, 111 a ra- Percent fiuoroethylene-saturatedaqueous charge, identical quan- The specific melt viscosities of thehexafluoropropylene- K of high molecular weight dispersion {68in weremodified resins of Examples 14 to 16 ranged from about tamed at Ramonrate more than 11 tlmfis great- 10 to 1010 poises at 330 f resins d Theproduct, however, fractured in the extrusion perunder identicalconditions in the absence of modifier, the folmallce testspecific meltviscosity was about 10 10 poises. The M E 26 lower melt Viscosity i in timprovement of the The procedure of Example 10 was repeated except thatdegree of sintering obtained during a fixed thermal treat- HFP ispremixed with the tetrafluoroethylene feed at a ment. concentration of0.9 weight percent. A product of 38.5

EXAMPL 24 percent solids, having an average particle size of 0.162micron and an SSG of 2.220, was obtained at an overall Th6 Procedure ofExample 22 was repeated that reaction rate of 529 grams/liter/hour. Inthe extrusion the hexafluompropylene was not Introduced unm performancetest, the resin yielded extrudate of quality Percent of totaltetrafluomeithylene to be reacted 10 at a pressure of 290 kg./cm. Inseparate tests, under been polymenzedresultmg Product of Welght the samegeneral conditions with a smaller die, the resin percent sol1ds wasobtamed at an overall reaction rate gave cxtrudate of quality 8 at areduction ratio of 10,000 of 585 grams/h had an average P slze of 60 to1 and an extrusion pressure of 845 kg/cmF. In fur- 0.182 Inlcr n an aSSG Of In the extrusfon ther analyses, the product of this example wasfound to formanc eX'mlded at 470 kgjcm-z to Yield have a value of Ad/z/d of less than 0.4 and a hexatrudate of quality 6. Infra-red analysesof the final prodfluoropmpylene content of 01 percent in the outer notand of a sample withdrawn after 70 percent of the 30 Weight percent ofthe resin panticleS total tetrafluoroethylene had reacted showegtacombitned EXAMPLES 27 AND 28 hexafluoropropylene content l P gf: Thegeneral procedure of Examples 1 to 12 was rethe outer 30 weflghtPfircent portion 0 c peated in a reactor of about the same capacity,having a In a companson run under the condltlons 0 .Xamp elength-to-diameter ratio of 2.6/1, the aqueous charge except that thegaseous it was replaced Wlth Pure occupying half the reactor volume andbeing agitated at tetrafluoroethylene 1n polymerizing the last 4 5percent of 95 I'PJL PPTE modifier was added in the concemra thetetrafluoroethylene polymerized, resin WhlCh fractured tions indicated,as a Percent of the aqueous charge, in the extrusion test was obtained.The overall reaction for: pressuring with t nfl th l and thereafter ratein this Comparison 11111 was 555 grams/ litfif/ only tetrafluoroethylenewas added. The supply of tetrain the absence of modifier under otherwiseidentical confiuoroethylene was shut 011 during polymerization of theditions, the overall reaction rate was 764 grams/liter/hour. last 2 0percent of the tetrafluoroethylene polymerized,

9 during which time the pressure decreased to 13 atmospheres absolute.Results are summarized in Table III.

0.49 and 0.44, respectively, and the fi /fi ratios were 4.6 and 2.3.

Table III Initiator Dispersing Extrusion Reaction Agent Overall PercentPerformance Example Tern- Percent Percent Reaction Solids No. pera-Modi- Wax Rate, in Disd v SSG ture, fier* g./liter/ persion ExtrusionExtru- Kind Percent C. Kind Percent hour Pressure, date kg./cm. Quality27 DSP 0.05 85 C9AFC 0.15 0.012 6.2 179 34. 9 0.143 2. 223 670 8 28 DSP0.05 85 O9AFC 0. 0.23 6. 2 135 34. 9 0. 146 2.184 830 2 In comparisonruns, made under identical conditions in the absence of modifier,identical quantities of high This application is a continuation-in-partof Serial Number 832,921, filed August 11, 1959.

Table IV d (Cor- Space- Extru- Melt Perrected, Distribu. Time sionQuality No.-avg. viscosity Ad%/ (rim) (M01. wt.) Example N0. cent d.7via Ultra- Width, Y1eld, Pressure, of Ex- SSG mol. wt. at 380 0. cshell/(mop Solids cfentr)i- Ad%, 1.: g./11ter/hr. kg./c1n. trndate (viaSSG) Poises t Core uge 29APS Initiator: 11 9 0.009 wt. percent, 0 60 0.;.010 wt. 2 percent methanol 43 4 modifier. -APS Initiator: 13- 0 0.006wt. percent, 18 7 70 0.; 0.009 wt. 5 percent methanol 4 modifier.

2.3% coagulum.

indicated the content of combined monomer other than tetrafluoroethylenein the resinous products of Examples 27 and 28 was in the range of 0.01to 0.3 weight percent.

EXAMPLES 29 AND 30 In the following examples, the procedure of Examples1-12 was followed except that the reactor and the degree of filling withaqueous charge of Examples 27 and 28 were used. Small samples of theliquid phase (contaming the dispersed particles of colloidalpolytetrafluoroethylene) were removed from the reactor at three separatetimes during the course of each run, in order that measurements ofsolids content, average particle size and SSG might be made. Thepolymeric product in each run was recovered and evaluated in the usualmanner, including determination of the particle size distributionWidths, Ad /2. Results are summarized in Table IV.

EXAMPLE 31 In the following example, the procedure and conditions ofExample 30 were used, except that the methanol modifier was added onlyafter the solids content of the liquid phase of the reactor had reached16.5 percent by weight. A sample withdrawn from the reactor just beforethe methanol was added had an SSG of 2.251. The high molecular weightdispersion resin produced, containing 40.0 percent solids by weight, wasobtained at an overall average rate of 450 g./liter/hour, had an averageparticle s ze of 0.19 micron and an SSG:2.234. In the extrusionperformance test, the resin yielded extrudate of quality 4 at anextrusion pressure of 420 kg./cm. The resin had a Ad /z /d, value of0.47, and an H /H of 2.1.

In two comparison runs made using a procedure identical with that ofExample 30, but using DSP initiator and with no modifier present, and atreaction temperatures of 85 and 110 C. respectively, the productsobtained in each case fractured in the extrusion performance test. TheAd /z/d values for these resins were sisting of tetrafluoroethylene,perfluoroalkyl triflnoroethylenes of 3 to 10 carbon atoms, andoxyperfluoroalkyl trifluoroe-thylenes of 3 to '10 carbons as combinedmonomer and comprising at least 98 Weight percent combinedtetrafluoroethylene, predominantly comprising spheroidal particles 0.05to 0.5 micron in diameter, having an average particle diameter in therange of 0.12 to 0.35 micron, a standard specific gravity of less than2.235, and a specific melt viscosity of at least 1x10 poises at 380 C.,said resin being one obtained by subjecting tetrafluoroethylene topolymerizing conditions of temperature and pressure in an aqueous mediumhaving dis solved therein a free-radical polymerization initiator, adispersing agent, and, present at least during and coextensively withthe polymerization of the final 30 percent of the tetrafluoroethylenepolymerized, a modifier in amounts ineffective to prevent resin havingthe aforesaid characteristics from being obtained, but cumulativelyeffective to maintain the overall rate of polymerization at least 5percent below that obtaining for the polymerization of an equal quantityof tetrafluoroethylene in an identical reaction medium continuouslysaturated With tetrafluoroethylene at the same temperature and pressurein the absence of said modifier, said modifier being selected from thegroup consisting of non-polymerizable chain transfer agents containingat least one covalentlybound non-metallic monovalent atom other thanfluorine, perfluoroalkyl trifluoroethylene of 3 to 10 carbon atoms, andoxyperfluoroalkyl trifluoroethylenes of 3 to 10 carbon atoms.

2. A particulate polytetrafluoroethylene resin, predominantly comprisingspheroidal particles 0.05 to 0.5 micron in diameter, having an averageparticle diameter in the range of 0.12 to 0.35 micron, a standardspecific gravity of less than 2.235, a specific melt viscosity of atleast 1 10 poises at 380 C., a ratio, to average particle diameter, ofthe spread in particle diameters at the halfpeak concentrations ofparticle size by Weight, of less than 0.40, and a ratio of numberaverage molecular Weight of the shell half to number average molecularweight of the core half of the resin particles of less than 3.5.

3. A particulate polymeric tetrafluoroethylene resin predominantlycomprising spheroidal particles 0.05 to 0.5 micron in diameter, havingan average particle diameter in the range of :12 to 0.35 micron, astandard specific gravity of less than 2.235, and a specific meltviscosity of at least 1X10 poises at 380 C., said resin consist-v ingessentially of tetrafiuoroethylene and hexafiuoropropylene as combinedmonomer and comprising at least 98 weight percent combinedtetrafiuoroethylene, and at least in the outer 30 weight percent of theresin particles, a combined hexafiuoropropylene content in the range of0.01 to 0.3 weight percent as determined by infra-red measurement.

4. A particulate polymeric tetrafluoroethylene resin, predominantlycomprising spheroidal particles 0.05 to 0.5 micron in diameter, havingan average particle diameter in the range of 0.12 to 0.35 micron, astandard specific gravity of less than 2.235, a specific melt viscosityof at least 1 10 poises at 380 C., and a ratio, to average particlediameter, of the spread in particle diameters at the half-peakconcentrations of particle size by weight, of less than 0.40, said resinconsisting essentially of tetrafiuoroethylene and hexafiuoropropylene ascombined monomer and comprising at least 98 weight percent combinedtetrafluoroethylene and, at least in the outer 30 weight percent of theresin particles, a combined hexafluoropropylene content in the range of0.01 to 0.3 Weight percent as determined by infra-red measurement.

5. A particulate polymeric tetrafiuoroethylene resin, consistingessentially of fluoroethylene selected from the group consisting oftetrafiuoroethylene, perfluoroalkyl trifluoroethylenes of 3 to carbonatoms, and oxyperfiuoroalkyl trifluoroethylenes of 3 to 10 carbon atomsas combined monomer and comprising at least 98 weight percent combinedtetrafluoroethylene, predominantly comprising spheroidal particles 0.05to 0.5 micron in diameter, having an average particle diameter in therange of 0.12 to 0.35 micron, a standard specific gravity of less than2.235, and a specific melt viscosity of greater than 1X10 poises at 380C., said resin having the capacity when blended in weight proportions of81 to 19 with a saturated hydrocarbon of 10 to 11 carbon atoms having aviscosity of about 1.36 centipoises at 25 C., to be extruded at 30 C. ata rate of 23.5 grams per minute through a die conically tapering at anapex angle of 60 to a cylindrical orifice 0.08 cm. in internal diameterand 0.038 cm. in axial length, at a reduction ratio of 1600/1 into acontinuous extrudate.

6. A process which comprises subjecting tetrafiuoroethylene topolymerizing conditions of temperature and pressure in an aqueous mediumhaving dissolved therein a free-radical polymerization initiator and adispersing agent, said conditions being effective in said medium in theabsence of other dissolved material to polymerize thetetrafiuoroethylene and recovering a particulate polymerictetrafluoroethylene resin predominantly comprising spheroidal particles0.05 to 0.5 micron in diameter, having an average particle diameter inthe range of 0.12 to 0.35 micron, a standard specific gravity of lessthan 2.235, a specific melt viscosity of at least 1x10 poises at 380 C.and a combined tetrafiuoroethylene content of at least 98 weight percentcharacterized in that said medium also contains dissolved thereinpresent at least during and coextensively with the polymerization of thefinal 30 percent of the tetrafluoroethylene polymerized, a modifier, inamounts ineffective to prevent resin having the aforesaidcharacteristics from being obtained but cumulatively efiective tomaintain the overall rate of polymerization at least 5 percent belowthat obtaining for the polymerization of an equal quantity oftetrafiuoroethylene in an identical reaction medium continuouslysaturated with tetrafluoroethylene at the same temperature and pressurein the absence of said modifier, said modifier being selected from thegroup consisting of non-polymerizable chain transfer agents containingat least one covalentlybound non-metallic monovalent atom other thanfluorine, perfiuoroalkyl trifluoroethylenes at 3 to 10 carbon atoms, andoxyperfluoroalkyl trifiuoroethylenes of 3 to 10 carbon atoms.

7. A process according to claim 6 wherein said modifier as addedconsists of methanol.

8. A process according to claim 6 wherein said modifier as addedconsists of hexafiuoropropylene.

9. A process according to claim 6 wherein said modifier as addedconsists of a mixture of methanol and hexafiuoropropylene.

10. A process according to claim 8 wherein the hexafluoropropylene ispresent only during the polymerization of the final half of thetetrafluoroethylene polymerized.

11. A process according to claim 7 wherein the methanol is present onlyduring the polymerization of the final half of the tetrafiuoroethylenepolymerized.

References Cited in the file of this patent UNITED STATES PATENTS2,549,935 Sauer Apr. 24, 1951 2,750,350 Kroll June 12, 1956 2,965,595Brinker et al. Dec. 20, 1960 2,965,619 Honn Dec. 20, 1960 3,010,950Thomas Nov. 28, 1961 FOREIGN PATENTS 789,786 Great Britain Jan. 29, 1958OTHER REFERENCES Dixon et al.: Ind. and Eng. Chem., volume 49, No. 10,pages 1687-1690, October 1957.

1. A PARTICULATE POLYMERIC TETRAFLUOROETHYLENE RESIN, CONSISTINGESSENTIALLY OF FLUOROETHYLENE OF THE GROUP CONSISTING OFTETRAFLUOROETHYLENE, PERFLUOROALKYL TRIFLUOROETHYLENES OF 3 TO 10 CARBONATOMS, AND OXYPERFLUOROALKYL TRIFLUOROETHYLENES OF 3 TO 10 CARBONS ASCOMBINED MONOMER AND COMPRISING AT LEAST 98 WEIGHT PERCENT COMBINEDTETRAFLUOROETHYLENE, PREDOMINANTLY COMPRISING SPHEROIDAL PARTICLES 0.05TO 0.5 MICRON IN DIAMETER, HAVING AN AVERAGE PARTICLE DIAMETER IN THERANGE OF 0.12 TO 0.35 MICRON, A STANDARD SPECIFIC GRAVITY OF LESS THAN2.235, AND A SPECIFIC MELT VISCOSITY OF AT LESAT 1X10**9 POISES AT380*C., SAID RESIN BEING ONE OBTANED BY SUBJECTING TETRAFLUOROETHYLENETO POLYMERIZING CONDITIONS OF TEMPERATURE AND PRESSURE IN AN AQUEOUSMEDIUM HAVING DISSOLVED THEREIN A FREE-RADICAL POLYMERIZATION INITIATOR,A DISPERSING AGENT, AND, PRESENT AT LEAST DURING AND COEXTENSIVELY WITHTHE POLYMERIZATION OF THE FINAL 30 PERCENT OF THE TETRAFLUOROETHYLENEPOLYMERIZED, A MODIFIER IN AMOUNTS INEFFECTIVE TO PREVENT RESIN HAVINGTHE AFORESAID CHARACTERISTICS FROM BEING OBTAINED, BUT CUMULATIVELYEFFECTIVE TO MAINTAIN THE OVERALL RATE OF POLYMERIZATION AT LEAST 5PERCENT BELOW THAT OBTAINING FOR THE POLYMERIZATION OF AN EQUAL QUANTITYOF TETRAFLUOREOTHYLENE IN AN IDENTICAL REACTION MEDIUM CONTINUOUSLYSATURATED WITH TETRAFLUOROETHYLENE AT THE SAME TEMPERATURE AND PRESSUREIN THE ABSENCE OF SAID MODIFIER, SAID MODIFIER BEING SELECTED FROM THEGROUP CONSISTING OF NON-POLYMERIZABLE CHAIN TRANSFER AGENTS CONTAININGAT LEAST ONE COVALENTLYBOUND NON-METALLIC MONOVALENT ATOM OTHER THANFLUORINE, PERFLUOROALKYL TRIFLUOROETHYLENE OF 3 TO 10 CARBON ATOMS, ANDOXPERFLUOROALKYL TRIFLUOROETHYLENES OF 3 TO 10 CARBON ATOMS.
 3. APARTICULATE POLYMERIC TETRAFLUOROETHYLENE RESIN PREDOMINANTLY COMPRISINGSPHERODIAL PARTICLES 0.05 TO 0.5 MICRON IN DIAMETER, HAVING AN AVERAGEPARTICLE DIAMETER IN THE RANGE OF 0.12 TO 0.35 MICRON, A STANDARDSPECIFIC GRAVITY OF LESS THAN 2.235, AND A SPECIFIC MELT VISCOSITY OF ATLEAST 1X10**9 POISES AT 380*C., SAID RESIN CONSISTING ESSENTIALLY OFTETRAFLUORETHYLENE AND HEXAFLUOROPROPYLENE AS COMBINED MONOMER ANDCOMPRISING AT LEAST 98 WEIGHT PERCENT COMBINED TETRAFLUOROETHYLENE, ANDAT LEAST IN THE OUTER 30 WEIGHT PERCENT OF THE RESIN PARTICLES, ACOMBINED HEXAFLUOROPROPYLENE CONTENT IN THE RANGE OF 0.01 TO 0.3 WEIGHTPERCENT AS DETERMINED BY INFRA-RED MEASUREMENT.